1. Field of the Invention
The present invention relates to a focus detecting apparatus for, e.g., a camera.
2. Description of the Prior Art
In one of conventional focus adjusting apparatuses for a camera, an exit pupil of a photographing lens is divided into two areas by a focus detecting optical system, and two images of an object to be photographed formed by light beams transmitted through the respective pupil areas are received by photoelectric conversion element arrays (e.g., CCD sensor arrays), respectively. Then, a focusing state of the photographing lens is detected in accordance with outputs from the respective sensor arrays, thereby driving the photographing lens on the basis of a detection result.
In the above focus detecting operation, if contrast of the object to be photographed is sufficient, focus detecting can be performed with high accuracy. However, if the contrast is low, focus detecting is impossible. Therefore, as a countermeasure against this problem, a so-called "searching operation" in which the photographing lens is driven independently of a detection result to increase the contrast of the object to be photographed is often performed.
The reason for this is as follows. That is, although the contrast may be low because the contrast of the object to be photographed is originally low, it may be reduced since a defocus amount of the photographing lens is large.
However, in the above searching operation, the photographing lens is normally reciprocated by turning its measuring ring between a nearest end and an infinite end. Therefore, when a telephoto lens is attached to the camera and the object to be photographed is dislocated from a so-called distance measuring frame in a viewfinder by, e.g., hand vibrations, the contrast is reduced, and the searching operation is immediately performed. As a result, it takes a long period of time to focus the object to be photographed after reciprocation.
In addition, in the above searching operation, the lens is driven after it is reciprocated once, resulting in a time-consuming operation. Therefore, if the searching operation is performed during so-called continuous photographing, a shutter chance may be missed.
Moreover, in the conventional searching operation, the lens is moved to a nearest or infinite position after it is reciprocated once, thereby stopping the searching operation. However, in many cases, an object to be photographed is located at a position immediately before the searching operation is started. Therefore, when the lens is stopped at the nearest or infinite position after the searching operation, the lens may be located at a position away from a position of the object to be photographed.